1. Field of the Invention
The present invention relates to a power amplifying circuit that amplifies a high-frequency signal, and also to a high-frequency module that includes the power amplifying circuit.
2. Description of the Related Art
As front-end modules for communication terminals, various types of high-frequency modules have been devised which include a power amplifying circuit that amplifies a high-frequency signal.
Japanese Unexamined Patent Application Publication No. 2010-68078 describes a high-frequency amplifying circuit in which output power is controlled through feedback control by a directional coupler. The high-frequency amplifying circuit includes a power amplifier that amplifies a high-frequency signal. An output terminal of the power amplifier is connected to the directional coupler, which includes a main line and a subline coupled to each other. An output signal from the power amplifier is transmitted through the main line and output to a load, such as an antenna. A part of the output signal transmitted through the main line propagates through the subline. The signal transmitted through the subline is detected. In accordance with a result of the detection, an amplification factor of the power amplifier is controlled.
In the configuration described above, where every output signal from the power amplifier passes through the directional coupler, power propagates through the subline depending on the degree of coupling between the main line and the subline in the directional coupler. Since power propagating through the subline is not output from the high-frequency amplifying circuit to a load, such as an antenna, output power from the high-frequency amplifying circuit may be reduced depending on the degree of coupling of the directional coupler.